Motor.



No. 686 ,l52.

Patented Nov. 5, I901. A. W. SMITH.

MOTOR (Application filed Sept. 9, 1901. (No Model.)

nth 1. 6388 UNITED STATES PATENT OFFICE.

ALBERT W. SMITH, OF WASHINGTON, DISTRICT OF COLUMBIA.

MOTOR.

SPECIFICATION forming part of Letters Patent No. 686,152, dated November5, 1901.

Application filed September 9, 1901. Serial No. 74,856. (No model.)

To ctZZ whom, it may concern:

Be it known that I, ALBERT W. SMITH, a citizen of the United States,residing at lVashington, in the District of Columbia, have invented anew and useful Improvement in Induction-Motors, of which the followingis a specification.

My invention relates to the squirrel-cage type of windings; and itsobject is to prevent lagging of the armature-current behind the inducingmagnetism.

With induction-motors having distributed field-windin gs the inductiverelation between a squirrel-cage winding and the field-coils is suchthat their respective currents should mutually compensate or balanceeach other, as in transformers, and the armature-current ought thereforeto be in phase with the magnetism. As is well known, however, thearmature-current lags abnormally, being subject both to greatself-induction and inferior conductivity. defects are due to a cancelingefiect between the parallel acting but unequal electromotive inventionconsists in preventing this cancellation by electrically separating theadjacent armature-bars from each other. To obtain this result, I employa plurality of end rings at each end of the armature and connect some ofthe bar ends in pairs thereto, while other bar ends are connected singlytherewith.

grammatic end view of an armature embodying my invention. Fig. 2 is awinding diagram of Fig. 1. Figs. 3 and 4 show modifications of myinvention, and Fig. 5 is an explan atory diagram.

In all the views the same characters refer to like or correspondingparts.

a is the armature-core, wound with bars 2 3 4, &c.

Z) and b areend rings connecting the front ends of the armature-bars,and c and c are rings joining the back ends of the bars.

01 is the field-core, wound with coils e and f.

The cause and effects of lagging armaturecurrents are explained byreference to Fig. 5, which is a diagram of a standard type of motorhaving a single bus-ring b at each end of the armature, thusconstituting the ordinary squirrel-cagewinding. Whilecurrentispassingthrough coils e and f, as per arrow-heads I have discovered that thesethereon, parallel acting electromotive forces of unequal strength, asindicated by arrows g, are induced in the armature-bars, the bars 4 and12 having the greatest electromotive forces, as represented by longarrows, and adjoining bars having lesser electromotivo forces, assymbolized by shorter arrows. By the law of parallel circuits havingunequal electromotive forces all of the inferior electromotive forcesare canceled by the superior electromotive forces of bars l and 12, inwhich the entire current therefore concentrates,th us enabling itspowerful magnetomotive force to set up the local self-inductive fields hand cause abnormal leakage of the main fields, as shown at 11. Theimmediate efiect on the armature of the local field h is to induce acounter electromotive force of self-induction (see arrow as) in bar a.The field 7t and counter electromotive force at will increase until thecounter electromotive force a: depresses the effective electromotiveforce of bar 4 to parity with the electromotive forces of bars 3 and 5,

y when equal but badly-dephased currents will forces in the severalarmature-bars; and my I flow through the bars 3, 4, and 5 in parallel.Time is an important element in the equalizing process just described.It can therefore occur only when the armature is at rest or when movingslowly, as at starting. With the armature in rapid motion, as per arrow19, any given bar, as bar 4:, can have the maximum electromotive forceand entire armature- In the drawings herewith, Figure 1 is a dia- 1current for a very brief time only, each successive bar as it becomessuperior in electromotive force setting up its own self-inductive fieldhand choking the current until the maximum point on the magnetic wave isreached, when the working current, lagging by a quarter-period, beginsto flow in the bar or several bars when very close together, which lasthad the greatest electromotive force. It is thus seen that practicallythe entire armature-current is crowded through a single bar of limitedconductivity, thus permitting its magnetomotive force to act locally,causing abnormal current lag and the large resistance losses whichcharacterize the squirrel-cage winding. So much of the main field as isgenerated in the field-slot opposite the field It is entirely blown backand caused to leak, as per flux-line t', through the air-gap andfield-slot, as shown, and the only way to reduce this leakage is todecrease the amount of field generated per slot by increasing the numberof slots per pole. Some of the main field is also caused to leak, as perflux-line 2'.

Having briefly explained the defects of the squirrel-cagewinding,myimprovementtherein will now be explained by reference to Figs.1 and 2.

At the front end of the armature alternate single bars are connected tothe same ring Z) and the remaining bars are connected to the ring 6. Atthe back end alternate pairs of adjacent bars are connected to ring 0and the remaining pairs are connected to ring 0. It is thus seen that atthe front end adjacent bars are electrically separated from each otherand that at the back adjacent pairs of bars are separated. I have shownthat with the ordinary squirrel-cage winding, Fig. 5, but one set ofbars (bars 4 and 12) can be fully active. With the connections shown inFigs. 1 and 2 there are four sets of bars fully active at all times. Inexplanation of this the current-paths of the several bars will now betraced.

The current of bar 4 flows through ring I) to and back through bar 12and through ring 0 back to bar 4. The current of bar 5 flows via ring I)to and through bar 13 and via ring 0 back to bar 5. The current-path ofbar 3 is through ring 5 to and through bar ll and by ring 0 back to bar3, and the current of bar 6 flows through ring I) to and through bar 14and by way of ring 0' back to bar 6.

The number of active bars per pole depends upon the span of any twobars, as bars 2 and 6, connecting both at their front and back ends tothe same rings. It will be seen that if an electromotive force existedin bar 2 it would, except when exactly equal to that of bar 6, eithercancel or be canceled by that of bar 6, and the current is thereforelimited to four bars-viz, one of the spanning-bars, as bar 6, and thespanned bars 3, 4, and 5. It is thus seen that with two rings at eachend of the armature four fully active bars per pole are obtained. Thisnumber will generally be sufficient. When more active bars are desired,it is only necessary to use more rings at the back end of the armature.In Fig. 3 is shown a bar-winding having three back rings 0, c, and 0',thus making the circuit-span between any two rings seven bars and givingsix fully active bars, as shown by arrows. In Figs. 1, 2, and 3 all theback ends of the bars are paired-tl1at is, two adjacent ends areconnected to the same ring and succeeding pairs of ends to differentrings, while at the front alternate ends are connected singly todilferent rings. In Fig. 4 is shown a modification having both singleand paired ends at each end of the armature, the single ends are,however, kept electrically separated from the paired ends by connectingall the single ends at the front to the same ring I), while all those atthe back connect to the same ring 0' all of the paired ends at the frontconnect to the same ring I), while at the back succeeding pairs connectto different rings. This construction is electrically equivalent to thatof Fig. 3, the circuit-span between any two rings being the same andgiving the same numherviz., six'-of active bars, as shown by arrows.

Having now fully explained my construction, it will be seen that eachset of cooperating bars, as bars 5 and 13, Figs. 1 and 2, haspractically an independent path, and no interference can therefore existbetween parallel acting but unequal electromotive forces, and thearmature-currents will therefore be more nearly in phase with theinducing magnetism. Also since the current is not confined to a singlebar the conductive losses peculiar to the squirrel-cage winding areobviated.

It will be seen that my invention is characterized by the employment ofa plurality of rings at each end of the armature, also by connectingsome of the bar ends singly to the rings, while other ends are connectedin pairs thereto. I have also shown that all bars at one end may besingly connected, while all bars at the other end are paired, or, as inFig. 4, that the same result is obtained by paired bars and single barsalternating at each end of the armature. My invention is therefore notto be narrowly construed; but

hat I claim as my invention is 1. The combination with the bars, orother winding elements, of an induction-motor armature, or secondary, ofa plurality of end rings at each end of the armature, forinterconnecting the ends of said bars, to form independent current-pathsfor adjacent bars, as set forth.

2. The combination with the bars of an induction-motorarmature, of aplurality of end rings at each end of the armature, some of the bar endsbeing connected in pairs to said rings, and the remaining bar ends beingconnected singly therewith, as set forth.

3. The combination with the bars of an induction-motor armature, of tworings at the front end thereof, alternate bars connected to the samering, and the remaining bars c011- nected to the other ring, two 01'more rings at the back end of the armature, and pairs of adjacent barsconnected to said rings, succeeding pairs of bars being connected todifferent rings, as set forth.

4. The combination with the bars of an induction-motor armature, of tworings at the front end thereof, alternate bars connected to the samering, and the remaining bars connected to the other ring, two rings atthe back end of said armature, alternate pairs of adjacent barsconnected to the same ring, and the remaining pairs of adjacent barsconnected to the other ring, as set forth.

ALBERT W. SMITH.

Witnesses:

WARREN C. STONE, MAUDE M. HARRISON.

